A method of using a flat panel display typified by a liquid crystal display (LCD) having a matrix of pixels arranged on a two-dimensional plane and light ray control elements in combination is known as a three-dimensional image display device method. The method is called a three-dimensional image display device method without glasses; the directions of the light rays emitted from the pixels of the flat panel display are limited by the light ray control elements and parallax information responsive to the emission direction is presented to the pixels, whereby the observer is allowed to observe an image responsive to the horizontal or vertical position of the observer and recognize a three-dimensional image.
The light ray control elements include a lenticular sheet, a lens array, slits, a pinhole array, etc., for light ray direction control. For the lenticular sheet or the slits, the lens ridge line expands in the vertical direction viewed from the observer.
The three-dimensional image display device method without glasses is characterized by the fact that the area in which the observer can observe a three-dimensional image is limited. That is, the number of pixels that can be provided per light ray control element is limited and therefore the area in which an image responsive to the observation direction can be provided (the area is referred as “viewing zone”) is also finite and if the observer is placed out of the area, he or she cannot observer the correct three-dimensional image.
In addition, a spectacle-type three-dimensional image display device method is known wherein the observer is made to wear spectacles and shuttering of left and right eyes and display switching are synchronized with each other for allowing the observer to recognize a parallax image conforming to both eyes of the observer. A spectacle-type three-dimensional image display device method is also known wherein while parallax images corresponding to the positions of both eyes of the observer are presented at the same time on the display, a micropole is used to make polarization directions orthogonal and polarizing plates with the polarization directions made orthogonal are provided in front of the left and right eyes of the observer, thereby presenting any desired parallax image to both eyes of the observer.
The spectacle-type three-dimensional image display device method is characterized by the fact that an image responsive to the observation position cannot be displayed (the observer cannot observer a three-dimensional image as he or she turns around the image=motion parallax does not exist) although the area in which the observer can observe a three-dimensional image is not limited. To overcome the problem, a method of realizing motion parallax by tracking the position of the head of the observer and switching the display in response to the position of the head is also available.
The three-dimensional image display device methods are common in that it is necessary to make the observer observe image acquired from more than one direction at the previously assumed observation position roughly matching the image acquisition direction to make the observer recognize a three-dimensional image.
The method of combining the light ray control elements with the display and switching the image in response to the observation position for the observer to observe the image corresponding to the observation position is the naked eye type method. The method of making the observer wear spectacles and shuttering the spectacles in synchronization with display switching for switching the parallax image displayed alternately on the display in response to the left and right eyes of the observer and the observation position of the observer is the spectacle type method.
The methods described above are common in that the images acquired from more than one direction are used to make the observer recognize a three-dimensional image. Thus, there are the points to be considered to acquire images more than one direction. Here, the points will be discussed as compared with two-dimensional image acquisition to reproduce a two-dimensional image.
When capturing and reproducing a two-dimensional image, the relationship between the capturing range and the reproduce range can be figured out easily. That is, the range defined by the viewing angle of the camera (=size of projection plane) is captured and is reproduced. Focus is achieved in the range of the depth of field and as capturing goes out of focus, a defocused image results.
In contrast, when capturing and reproducing a three-dimensional image, the capturing range of a camera array and the limit of depth defined by a display device need to be considered.
In the simplest case, the angles of view of a camera array are overlapped in the range corresponding to the display surface. In this case, the area in which the capturing ranges of the two cameras outermost placed overlap corresponds to the area always displayed on the display device while the observer is in the viewing zone if a three-dimensional image is reproduced. The area in which the capturing ranges do not overlap corresponds to the area which may or may not be seen as the frame of the display device hinders even when the observer observes in the viewing zone.
In a naked-eye-type stereoscopic display, the limit of depth corresponds to a “display limit” that is described in the following reference R1.
R1: “Analysis of resolution limitation of integral photography” H. Hoshino, et al., J. Opt. Soc. Am. A., 15 (8), 2059 (1998)
As a three-dimensional image is displayed with the display limit as a guideline, the image quality that can sustain observation can be maintained. On the other hand, a spectacle-type three-dimensional image display device involves the pop-up amount limit defined in the sense of preventing fatigue caused by mismatch between congestion and adjustment.
For example, in some 100-inch twin-lens projection types of display device, when the viewing distance (L) is set to 3 m, the near-side limit is set to 500 mm and the far-side display limit is set to 1500 mm. In some twin-lens mobile telephone screens, the near-side limit is set to 80 mm and the far-side display limit is set to 160 mm. Thus, often the near-side limit is suppressed to about one-sixth the viewing distance and the far-side display limit is suppressed to about a half the viewing distance.
However, the suppression is determined due to the demands from a side of the three-dimensional image display device, and cannot be operated from the camera array side. Modifying the perspective projection degree or modifying the size is well known as the effect in capturing and reproducing a two-dimensional image. Specifically, the image captured at a position closer to the object than the observation position at the reproduce time becomes an image high in the perspective degree, and the image captured at a position more distant than the observation position becomes an image low in the perspective degree as it is captured with a zoom lens. Thus, the behavior of object over one camera can be understood comparatively by intuition.
On the other hand, in three-dimensional image display device, the direction in which a parallax image is acquired and the direction in which parallax information can be observed are completely matched, whereby the captured object is reproduced intact. However, representation can be made in such a manner that the perspective degree of the object is modified or thickness is modified (as such described in reference R2) or the size is modified by intentionally deviating from the relationship.
R2: “Distortion Control in a One-Dimensional Integral Imaging Autostereoscopic Display System with Parallel Optical Ray Groups” T. Saishu, et al., SID 04 Digest, 1438 (2004)
However, each multi-view image captured with a camera array and the image reproduced in a three-dimensional image display device are difficult to understand by intuition. For example, if the capturing interval of the camera array is halved, the thickness of the object-displayed on the three-dimensional image display device becomes roughly a half as compared with the case where the display thickness when the capturing interval is not halved is “1”. To reproduce a three-dimensional image low in the perspective degree, it is necessary to extend the capturing distance and enlarge the camera-to-camera spacing in proportion to the expanded capturing distance and at the same time, modify the viewing angle so as to maintain the size of the projection plane.
Unlike a single camera used for capturing a two-dimensional image, the behavior of the camera array is difficult for the object user who creates three-dimensional image, to understand by intuition. If the object user understands, operation of moving and relocating the cameras becomes intricate as the number of the cameras increases.